The present invention relates to a cooler device in a vehicle according for cooling both compressed air and recirculating exhaust gases.
The amount of air which can be supplied to a supercharged combustion engine depends on the pressure of the air but also on the temperature of the air. Supplying the largest possible amount of air to the combustion engine therefore entails cooling the compressed air in a charge air cooler before it is led to the combustion engine. The compressed air is usually cooled by ambient air flowing through the charge air cooler. The compressed air can thus be cooled to a temperature substantially corresponding to the temperature of the surroundings.
The technique known as EGR (Exhaust Gas Recirculation) is a known way of leading part of the exhaust gases from a combustion process in a combustion engine back, via a return line, to an inlet line for air supply to the combustion engine. A mixture of air and exhaust gases is thus supplied via the inlet line to the engine's cylinders in which the combustion tales place. The addition of exhaust gases to the air causes a lower combustion temperature resulting inter alia in a reduced content of nitrogen oxides NOx in the exhaust gases. This technique is applied in both Otto engines and diesel engines. The returned exhaust gases are usually cooled in a so-called EGR cooler. In a conventional EGR cooler, the exhaust gases are cooled by the coolant circulating in the vehicle's cooling system which also cools the combustion engine. The EGR cooler is thus subject to the limitation that the exhaust gases cannot be cooled to a lower temperature than the coolant temperature, which is normally well above the temperature of the surroundings.
The cooled exhaust gases are therefore usually at a higher temperature than the cooled compressed air when they mix in an inlet line to the combustion engine. The mixture of air and exhaust gases which is led to the combustion engine will therefore be at a higher temperature than the compressed air led into a supercharged combustion engine which is not provided with equipment for recirculation of exhaust gases. The performance of a supercharged combustion engine provided with recirculation of exhaust gases will therefore be somewhat inferior to that of a supercharged combustion engine not provided with such recirculation.